The present invention relates to microchannel electrophoresis instruments, particularly to input sample insertion geometry of the microchannels, and more particularly to the input port geometry for planar microchannel arrays which include at least injector-concentrator electrodes that enable efficient extraction and injection of a sample from the input port.
Current emerging alternative methods to commercial slab-gel electrophoresis (e.g. for DNA sequencing) are systems based on discrete drift channels. One type is bundles of discrete glass micro-capillaries. Another type consists of one dimensional, integrated arrays of microchannel patterned in bonded glass plate pairs, such as described and claimed in U.S. Pat. No. 5,877,580 issued Mar. 2, 1999. The input sample insertion geometry involves a right angle connection to the microchannel, such as the typical prior art L-load input well for microchannel plates, or a T-load input well, such as described and claimed in copending application Ser. No. 09/178,778 filed Oct. 26, 1998, entitled A T-Load Microchannel Array and Fabrication Method, assigned to the same assignee. These right angle connections to the microchannel results in a three dimensional injection volume of the sample onto the end of the drift gel in the microchannel, which in turn, is a fundamental limit of resolution; the gel-loading buffer fluid interface is defined by convection and diffusion and is difficult to control, partially, because the input hole well overlaps the microchannel end. Also, the loading procedure such as sample size and exact location, insertion method, loading field, field geometrical dispersion, field modification by sample ions, excess sample flush, time delays before starting run, ionic current heating, etc., dramatically influences resolution because drift and diffusion during the loading process can dominate defining the initial injection volume.
The highest resolution has been obtained with electrokinetic (ek) loading directly onto a plane perpendicular to a micro capillary axis at its end; even so, the finite transition of gel to loading buffer and also sample self-diffusion is a limit to resolution; i.e. the loading plane has a finite thickness.
The present invention resolves these prior problems by providing electrodes for the L-load or the T-load for planar, high density, integrated, microchannel arrays. The invention enables higher resolution by concentrating the DNA sample into a narrow strip and holding it there until all the loading is finished and the run starts. Use of an optional second electrode can alleviate the adverse response of impurity ions often present in the DNA sample. An additional electrode may be located in or on the input hole to better define the initial loading.
It is an object of the present invention to provide an improved input port geometry for planar microchannel arrays.
A further object of the invention is to provide injector-concentrator electrodes for microchannel electrophoresis.
A further object of the invention is to provide an input port geometry which utilizes injector-concentrator electrodes for microchannel arrays that enables efficient extraction and injection of the DNA sample from a single input port.
Another object of the invention is to provide an injector-concentrator electrode for both the L-load or the T-load microchannel electrophoresis configurations.
Another object of the invention is to improve the resolution of L-load or T-load microchannel instruments by electrodes positioned for concentrating the sample into a narrow strip and holding it there until all the loading is finished and the run starts.
Another object of the invention is to utilize an electrode to alleviate the adverse response of impurity ions often present in the example.
Another object of the invention is to provide an electrode in or on the input hole to better define the initial loading.
Another object of the invention is to provide an input port geometry which utilizes multiple electrodes to enable improvement in loading, separation, trapping, and concentration of a planar microchannel instrument.
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. Basically, the present invention provides an improved input geometry for planar microchannel arrays which utilizes electrodes to enable improved loading, separation, trapping, and concentration of samples. The electrode arrangement may be utilized with both L-load and T-load microchannel arrays. The invention results in: 1) higher resolution geometry-axially very narrow DNA injection into the channel, 2) more tolerant sample insertion procedure, 3) more tolerant of sample preparation impurities, and 4) efficient 2-D (e.g. Titer format) sample input and injection.